Composite pile and construction method thereof

Abstract

The invention relates to a composite pile and a construction method thereof and relates to the technical field of building pile foundations, the composite pile is composed of a prefabricated hollow pile and a concrete expanding body, and the concrete expanding body is arranged in the middle and / or at the bottom of the pile; when the composite pile is subjected to vertical pressure, the equal-strength area of the concrete expanding body is free of deformation, and stable, continuous and slowly-changing deformation occurs in the continuous-strength-reducing area. The construction method comprises the construction steps of pile sinking, hole forming and pouring. The columnar heavy body is moved downwards to extrude concrete in an inner hole cavity of the prefabricated hollow pile to enter a concrete pile section below the columnar heavy body, and a spherical carrier composed of an expanded-diameter hole cavity filled with the concrete, a compacted mixture layer and a compacted rock-soil layer is formed; the sunken prefabricated hollow pile penetrates through the middle carrier to form a pile middle concrete expanding body, and / or the sunken prefabricated hollow pile enters the concrete in the bottom carrier to form a pile bottom concrete expanding body, and the top elevation of the composite pile is met. The technical scheme provided by the invention has the effects of wide stratum adaptability, high pile bearing capacity and low pile cost.

Description

Technical Field

[0001] The invention relates to a composite pile and a construction method thereof, belonging to the technical field of building pile foundation construction. Background Art

[0002] In the existing building pile foundation, precast hollow piles are widely used, especially precast concrete pipe piles. Cement soil and precast concrete pipe piles are usually combined to form cement soil composite piles as pile foundations. The bearing capacity of the composite piles is improved by increasing the effective surface area of ​​the composite piles. It is mainly suitable for clay, silt, sand and other strata. Its disadvantages are: first, the cement soil needs to be mixed on site, which is expensive, inefficient, poorly uniform, and pollutes the environment. Second, there is residue at the bottom of the composite pile and the end resistance is small. Improving the bearing capacity of the composite pile can only be achieved by increasing the pile length, and the pile foundation cost is high. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide a composite pile and a construction method thereof. The composite pile formed by the construction method has the effects of adapting to a wide range of strata, having a high pile bearing capacity and low pile cost.

[0004] In order to solve the above problems, the specific technical solutions of the present invention are as follows: a composite pile, which is composed of a precast hollow pile and a concrete enlarged body. There is at least one concrete enlarged body in the composite pile, and the concrete enlarged body can be arranged in the middle and / or bottom of the precast hollow pile. The precast hollow pile and the concrete in the concrete enlarged body are consolidated into one, and a certain distance is maintained between two adjacent concrete enlarged bodies; the concrete enlarged body is a spherical end carrier that directly wraps the outer surface of the precast hollow pile part; the concrete enlarged body is composed of an internal constant strength zone and a strength continuously reduced zone that wraps the constant strength zone, the constant strength zone is composed of compacted concrete, and the strength continuously reduced zone The low zone is a region where the strength of the compacted mixture layer and the compacted rock-soil layer decreases steadily and continuously from the inside to the outside. The compacted mixture layer is a mixture of concrete and rock-soil formed by compaction and mixing with a certain thickness. The compacted mixture layer is wrapped with an equal strength zone, and the compacted mixture layer is surrounded by a compacted rock-soil layer. In the process of diffusion and attenuation of the vertical pressure transmitted from the prefabricated hollow pile by the concrete expansion body, there is no deformation in the equal strength zone, and steady and continuous slow-varying deformation occurs in the zone of continuous strength reduction. In the static load test of the composite pile, within the allowable pile foundation settlement displacement, the Q-s curve of the static load test is a slow-varying type, and no obvious steep drop occurs.

[0005] The prefabricated hollow piles are prefabricated concrete hollow piles, prefabricated steel hollow piles or prefabricated steel and concrete composite hollow piles; the inner cavity of the prefabricated hollow piles can be provided with pull-out members or steel cages, and a certain amount of concrete can be poured.

[0006] A construction method for a composite pile according to claim 1, comprising the following steps: 1) Pile driving and hole pouring: Align the bottom end of the precast hollow pile with the pile position, sink the precast hollow pile to the top elevation of the concrete in the concrete expansion body at the bottom of the composite pile, place the spiral drill concentrically into the inner cavity of the precast hollow pile and rotate it to drill. First, drill the rock and soil that are crowded at the bottom end of the inner cavity of the precast hollow pile, and then drill the rock and soil below the precast hollow pile to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. Raise the spiral drill and pour concrete into the pile hole and the inner cavity of the precast hollow pile, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5m. 2) Forming an expanded cavity filled with concrete, a compacted mixture layer and a compacted rock and soil layer: Through vertical pressure, vibration or gravity drop, a columnar weight is moved downward to squeeze the concrete in the cavity of the precast hollow pile into the cylindrical pile hole filled with concrete, first squeezing and expanding the rock and soil wall at the upper end of the pile hole, then squeezing and expanding the rock and soil wall in the middle of the pile hole, and finally squeezing and expanding the rock and soil wall at the bottom end of the pile hole and the rock and soil on the bottom end face of the hole. In the process of squeezing and expanding the rock and soil of the pile hole wall, the downward-moving columnar weight squeezes the fluid concrete. The fluid concrete preferentially squeezes the rock and soil in the middle of the pile hole wall to expand to form the maximum diameter, squeezing and expanding the cylindrical pile hole into a cavity with small diameter expansion at the upper and lower ends and large diameter expansion in the middle, which is filled with compacted concrete, and a small amount of concrete is squeezed into the rock and soil of the cavity wall to form a compacted mixture layer. In the compacted mixture layer, the concrete content on the concrete side of the cavity closer to the expanded diameter is higher, and at the same time, a certain thickness of rock and soil outside the compacted mixture layer is squeezed. Densely form a compacted rock and soil layer. In the compacted rock and soil layer, the closer the rock and soil density is to the compacted mixture layer, the greater the density. The poured concrete is all used to compress the pile hole wall. The final extrusion stress on the concrete is not less than half of the rated extrusion strength of the hole wall of the PC pipe pile with the same outer diameter as the precast hollow pile to be constructed in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than the rated extrusion strength of the hole wall of the precast hollow pile to be constructed. The columnar weight is lifted to form a spherical carrier consisting of an equal strength zone composed of the compacted concrete in the expanded diameter hole, a continuously reduced strength zone composed of the compacted mixture layer and the compacted rock and soil layer, and a spherical carrier. After the composite pile is formed, in the process of diffusing and attenuating the vertical pressure transmitted from the precast hollow pile, there is no deformation in the equal strength zone, and a smooth, continuous and slow-changing deformation occurs in the continuously reduced strength zone. 3) Sinking the precast hollow pile into the compacted concrete in the enlarged diameter cavity to a certain depth that meets the top elevation of the composite pile; forming a composite pile with a concrete expansion at the bottom of the pile.

[0007] A composite pile construction method, wherein step 1) is replaced by bored pile sinking and pouring: at the center of the pile position, a pilot hole having a diameter smaller than the outer diameter or diagonal length of the cross section of a precast hollow pile is first drilled using a spiral drill, the pilot hole being drilled to a depth within a range of 1.5 to 4.0 times the outer diameter or diagonal length of the cross section of the precast hollow pile below the top elevation of concrete in an expanded concrete body at the bottom of the pile; then, a precast hollow pile is sunk at the pile position to squeeze and expand the pilot hole to the top elevation of concrete in the expanded concrete body at the bottom of the pile; and then, a certain amount of concrete is poured into the inner cavity of the precast hollow pile and the bottom of the pilot hole, ensuring that the concrete pouring height of the inner cavity of the precast hollow pile does not exceed 1.5 meters.

[0008] A composite pile construction method comprises the following steps: 1) aligning the bottom end of a precast hollow pile with the pile position, sinking the precast hollow pile to the top elevation of the concrete in the concrete enlarged body in the middle of the composite pile; concentrically placing a spiral drill into the inner cavity of the precast hollow pile and rotating the drill to first drill the rock and soil that are packed at the bottom end of the inner cavity of the precast hollow pile, and then drilling into the rock and soil below the precast hollow pile to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile; lifting the spiral drill to pour concrete into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is no more than 1.5 meters; 3) replacing the step by sinking the precast hollow pile through the enlarged diameter cavity filled with concrete, the compacted mixture layer, and the compacted rock and soil layer to form the concrete enlarged body in the middle of the pile; and 4) continuing to sink the precast hollow pile to meet the top elevation of the composite pile, thereby forming a composite pile with a concrete enlarged body in the middle of the pile.

[0009] After step 3), the precast hollow pile is continued to be sunk to the top elevation of the concrete in the second concrete enlarged body in the middle of the pile. The spiral drill is concentrically placed in the inner cavity of the precast hollow pile and rotated to drill. The bottom end of the inner cavity of the precast hollow pile is first drilled to fill the mixture of concrete, rock and soil and concrete. Then, the rock and soil below the precast hollow pile are drilled to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. The spiral drill is lifted and concrete is poured into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5 m. Then, steps 2) and 3) are repeated to form the second concrete enlarged body in the middle of the pile. By repeating the above process of forming the second concrete enlarged body in the middle of the pile, multiple concrete enlarged bodies in the middle of the pile can be formed.

[0010] A method for constructing a composite pile comprises the following steps: 1) aligning the bottom end of a precast hollow pile with the pile position, sinking the precast hollow pile to the top elevation of the concrete in the expanded concrete body in the middle of the composite pile, concentrically placing a spiral drill into the inner cavity of the precast hollow pile and rotating the drill, first drilling the rock and soil that is packed at the bottom end of the inner cavity of the precast hollow pile, and then drilling the rock and soil below the precast hollow pile to form a cylindrical pile hole, the pile hole depth being 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile, lifting the spiral drill, and pouring concrete into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is no more than 1.5m; and 3) sinking the precast hollow pile through the expanded diameter cavity filled with concrete, the compacted mixture layer, and the compacted rock. soil layer to form a concrete expansion body in the middle of the pile; step 4) continue to sink the precast hollow pile to the top elevation of the concrete in the concrete expansion body at the bottom of the composite pile, concentrically place the spiral drill into the inner cavity of the precast hollow pile and rotate and drill, first drill the concrete, rock and concrete mixture at the bottom end of the inner cavity of the precast hollow pile, and then drill the rock and soil below the precast hollow pile to form a cylindrical pile hole, the depth of the pile hole is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile, lift the spiral drill, and pour concrete into the pile hole and the inner cavity of the precast hollow pile, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5m; then, repeat steps 2) and 3) in claim 3) to form a composite pile with a concrete expansion body in the middle and bottom of the pile.

[0011] After step 3), the precast hollow pile is continued to be sunk to the top elevation of the concrete in the second concrete enlarged body in the middle of the pile. The spiral drill is concentrically placed in the inner cavity of the precast hollow pile and rotated to drill. The bottom end of the inner cavity of the precast hollow pile is first drilled to fill the mixture of concrete, rock and soil and concrete. Then, the rock and soil below the precast hollow pile are drilled to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. The spiral drill is lifted and concrete is poured into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5 m. Then, steps 2) and 3) are repeated to form the second concrete enlarged body in the middle of the pile. By repeating the above process of forming the second concrete enlarged body in the middle of the pile, multiple concrete enlarged bodies in the middle of the pile can be formed.

[0012] The enlarged cavity filled with concrete, the compacted mixture layer and the compacted rock and soil layer can be formed by pouring a certain amount of concrete into the cavity of the precast hollow pile once and then moving the columnar weight downward to squeeze the concrete. It can also be formed by pouring a certain amount of concrete into the cavity of the precast hollow pile twice or more and then moving the columnar weight downward to squeeze the concrete twice or more, and each time concrete is poured, the columnar weight moves downward once to squeeze the concrete and expand the cavity wall.

[0013] Anti-pullout parts or steel cages are placed in the inner cavity of the prefabricated hollow pile, and a certain amount of concrete is poured.

[0014] For sections where it is difficult to sink precast hollow piles, a spiral drill can be used to drill a pilot hole through the inner cavity of the precast hollow pile, and then the precast hollow pile can be sunk through the section.

[0015] The gravity fall of the columnar weight refers to the process of lifting the columnar weight to a certain height multiple times and letting it fall freely multiple times during the downward movement of the columnar weight after the concrete is poured once. The columnar weight squeezes the concrete once by free falling each time it is lifted. The upper end of the columnar weight is made into a cone shape with a small top and a large bottom. A lifting fixture is provided at the center of the columnar weight on the upper end surface for fixing one end of a rope. The other end of the rope is fixed on the drum of a slip-type winch. A certain fitting gap is retained between the outer surface of the columnar weight and the inner cavity wall of the precast hollow pile. Concrete can be poured through the fitting gap as a pouring channel during the lifting of the columnar weight or after the columnar weight is lifted and stayed at a certain height.

[0016] The concrete forming the concrete expansion body can be poured during the process of lifting the spiral drill or the columnar weight, or the spiral drill or the columnar weight can be lifted to the outside of the inner cavity of the prefabricated hollow pile and then poured.

[0017] This application adopts the above technical solution, which has the following advantages: 1. The concrete within the concrete enlargement in a composite pile is firmly bonded to the precast hollow pile, forming a single structure. This results in high end bearing capacity and low pile cost. When the concrete enlargement is located at the base of the pile, the depth of the precast hollow pile entering the concrete within the enlargement is typically at least 1 times the outer diameter of the precast hollow pile. For composite piles requiring pullout resistance, the precast hollow pile can penetrate even deeper, with the compacted concrete within the enlargement tightly wrapping around the outer surface of the precast hollow pile, forming a strong bond. The concrete enlargements in a composite pile can be located in the middle and / or bottom of the pile shaft. Each enlargement is relatively independent, each wrapped in layers, and connected together by the precast hollow pile. Independent enlargements offer high end resistance, and multiple independent enlargements provide even higher end resistance for composite piles. By installing multiple enlargements within a high-strength precast hollow pile shaft (no less than concrete strength grade C60), the pile length can be shortened most effectively, reducing pile construction costs.

[0018] 2. The concrete enlargement of the composite pile is a carrier with high strength in the center, and the surrounding strength decreases smoothly and continuously from the inside to the outside, meeting the requirements of the overall stability index. It has a large volume and good integrity. The strength structure of the concrete enlargement conforms to the smooth and continuous dispersed attenuation transmission of pressure and can bear large vertical loads. The strength continuous reduction zone of the concrete enlargement satisfies the requirement that the load force (pressure) transmitted by the equal strength zone is diffused and attenuated and then transmitted to the far end. This avoids stress concentration at the point where the strength drops sharply during the force transmission process, resulting in large deformation on the low-strength side and increased vertical displacement of the pile. The settlement displacement of the composite pile in this application is caused by the smooth and continuous slow-changing deformation of the strength continuous reduction zone and the smooth and continuous slow-changing deformation of the original rock and soil layer outside the strength continuous reduction zone. Within the allowable pile foundation settlement displacement, the overall slow change and stability of the pile settlement deformation are guaranteed, and no steep drop phenomenon will occur.

[0019] 3. In pile construction, the formation of the concrete expansion body is to first use a spiral drill to form a cylindrical pile hole, remove the rock and soil in the pile hole, then lift the spiral drill, pour concrete, and then move the columnar weight downward to squeeze the concrete in the hole of the prefabricated hollow pile to squeeze the concrete in the pile hole to form an expanded diameter cavity filled with concrete; the pile hole formed by spiral soil displacement drilling greatly reduces the amount of extruded soil movement in the process of forming the expanded diameter cavity, and also reduces the difficulty of forming the expanded diameter cavity, laying the foundation for forming an expanded diameter cavity with a larger diameter; make full use of the certain fluidity of concrete to achieve the maximum diameter expansion of the rock and soil in the middle of the pile hole wall, forming a concrete expansion body with small diameter expansion at the upper and lower ends and large diameter expansion in the middle; in the process of squeezing concrete and squeezing the pile hole wall, due to the certain sparseness of the pile hole wall soil, a small amount of concrete will be squeezed into the pile hole A compacted mixture layer is formed in the wall rock and soil, and at the same time, a certain thickness of rock and soil outside the compacted mixture layer is compacted; the downward-moving columnar heavy body squeezes the concrete with great pressure, and all the poured concrete is used to expand the pile cavity, so the effective utilization rate of concrete is high; the sparseness of the cylindrical pile hole and the rock and soil on the wall of the cylindrical pile hole that form the concrete expansion body is the basis for forming a larger volume of expanded diameter cavity filled with concrete, that is, the basis for forming a larger volume of equal strength zone composed of concrete and a large volume of continuously reduced strength zone composed of the compacted mixture layer and the compacted rock and soil layer; the concrete forming the concrete expansion body only uses a single strength grade, usually one of C25, C30, C35, and C40. Composite piles with high bearing capacity requirements and a small number of concrete expansion bodies in the composite piles use higher strength concrete, which improves construction efficiency.

[0020] 4. During the formation of the concrete expansion body, the integrity of the precast hollow pile and the quality of the composite pile can be guaranteed by reasonably controlling the squeezing force of the columnar weight on the concrete in the cavity of the precast hollow pile.

[0021] 5. The columnar weight used for construction can be hollow and equipped with a closable and openable door at the bottom. The door is closed when the columnar weight is moved down to squeeze the concrete, and is opened during the process of lifting the columnar weight. The concrete forming the concrete expansion body can be poured through the inner cavity of the columnar weight during the process of lifting the columnar weight, thereby improving construction efficiency.

[0022] 6. The lower end of the columnar weight used for construction can be designed into a frustum-like structure with a smaller bottom and a larger top, which is more conducive to radial compaction of concrete and expansion of the cavity wall rock and soil; the cross-sectional shape of the columnar weight is the same as or similar to the cross-sectional shape of the cavity of the prefabricated hollow pile being constructed, and a gap of 10-50mm is maintained between them; the gap is used as a concrete pouring channel, and concrete is poured during the process of lifting the columnar weight, which is conducive to improving construction efficiency.

[0023] 7. During construction, a gap of 10-50mm is maintained between the outer diameter of the spiral drill inserted into the inner hole of the prefabricated hollow pile and the inner hole wall of the prefabricated hollow pile, avoiding excessive contact between the spiral drill and the inner hole wall of the prefabricated hollow pile when drilling, thereby ensuring the verticality of the prefabricated hollow pile and ensuring the smooth upload of the soil generated by the drill when drilling.

[0024] 8. During construction, prefabricated hollow piles are directly sunk and then concrete expansion bodies are formed. The lateral resistance between the surface of the prefabricated hollow piles and the surrounding soil is high, and the construction efficiency is good.

[0025] 9. For complex geological conditions, such as rock and soil layers with low compressibility around the piles that cannot be penetrated by precast hollow piles, the method of first guiding a hole with an outer diameter or diagonal length smaller than the cross-section of the precast hollow pile and then sinking the pile is adopted, and then a concrete expansion body is formed at the bottom of the pile. Under the premise of maintaining a certain lateral resistance on the surface of the precast hollow pile, the range of rock and soil layers that the composite pile can adapt to is expanded.

[0026] 10. The composite piles of the present application have certain requirements for the final concrete extrusion force that forms the overall stable concrete expansion body, which ensures the gradual variation and stability of the composite pile settlement, without the sudden drop phenomenon, and also ensures the overall stability of the building (structure) structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of a composite pile structure with a concrete expansion at the bottom.

[0028] Figure 2 Schematic diagram of a composite pile structure with concrete expansion bodies in the middle and bottom.

[0029] Figure 3 This is a schematic diagram of the construction method of the composite pile in Example 1.

[0030] Figure 4 This is a schematic diagram of the construction method of the composite pile in Example 2.

[0031] Figure 5 Schematic diagram of the construction method of composite piles in Example 3.

[0032] Figure 6 Schematic diagram of the construction method of composite pile in Example 4 Figure 1 .

[0033] Figure 7 Schematic diagram of the construction method of composite pile in Example 4 Figure 2 .

[0034] Figure 8 Schematic diagram of the construction method of composite pile in Example 5 Figure 1 .

[0035] Figure 9 Schematic diagram of the construction method of composite pile in Example 5 Figure 2 .

[0036] Figure 10 Schematic diagram of the composite pile structure with anti-pullout parts inserted and concrete poured.

[0037] Figure 11 Schematic diagram of the composite pile structure with steel cage placed and concrete poured.

[0038] In the figure: 1-precast hollow pile, 2-auger, 3-compacted rock and soil, 4-cylindrical pile hole, 5-concrete, 6-columnar weight, 7-compacted concrete and rock and soil mixture, 8-pull-out member, 9-reinforcement cage, 11-compacted concrete, 12-compacted mixture layer, 13-compacted rock and soil layer, 14-original rock and soil layer, 15-umbrella-shaped body. DETAILED DESCRIPTION

[0039] The formation mechanism of the concrete expansion body of the present application is as follows: first, a spiral drill 2 is used to penetrate the inner cavity of the precast hollow pile 1 to form a cylindrical pile hole 4 with a certain depth (usually 1-4 times the outer diameter or diagonal length of the cross section of the precast hollow pile, the smaller value is taken for the precast hollow pile with a larger outer diameter and the larger value is taken for the precast hollow pile with a smaller outer diameter) below the bottom end of the precast hollow pile 1, and the rock and soil on the pile hole wall maintain a certain sparseness, and the spiral drill 2 is lifted to pour concrete into the cylindrical pile hole 4 and the inner cavity of the precast hollow pile 1, and the height of the concrete remaining in the inner cavity of the precast hollow pile 1 is kept not more than 1.5m. Then, the bottom end face of the downward-moving columnar weight 6 is used to squeeze the concrete in the inner cavity of the precast hollow pile 1, and the pressure concrete flowing out of the inner cavity of the precast hollow pile 1 first squeezes the concrete at the upper end of the cylindrical pile hole 4, forcing the rock and soil at the upper end of the cylindrical pile hole wall to be squeezed to form an enlarged diameter cavity and filled with concrete. When the extrusion force of the concrete is not enough to squeeze the enlarged diameter cavity and expand it again, the compressed concrete transmits force to the column The concrete in the middle of the cylindrical pile hole 4 squeezes the rock and soil in the middle of the cylindrical pile hole wall to form an enlarged diameter cavity and is filled with concrete. When the extrusion force of the concrete is not enough to squeeze the enlarged diameter cavity in the middle of the cylindrical pile hole 4 and expand it again, the compressed concrete transmits force to the concrete at the lower end of the cylindrical pile hole 4, squeezing the rock and soil at the lower end of the cylindrical pile hole wall and the bottom of the pile hole to form an enlarged diameter cavity and be filled with concrete. The columnar weight 6 moves down to the bottom end of the precast hollow pile 1 or enters a certain depth into the concrete in the enlarged diameter cavity. In the process of squeezing the concrete and expanding the rock and soil hole wall to form the enlarged diameter cavity, a small amount of concrete is squeezed into the rock and soil on the hole wall to form a compacted mixture layer 12. The closer the concrete side of the compacted mixture layer 12 is to the enlarged body, the higher the concrete content and the higher the strength. At the same time, a certain thickness of rock and soil outside the compacted mixture layer 12 is squeezed and compacted to form a compacted rock and soil layer 13. The closer the compacted mixture layer 12 is to the side, the greater the density of the compacted rock and soil is, the higher the strength is.In the process of forming the expanded diameter cavity filled with concrete, the downward-moving columnar weight 6 squeezes the fluid concrete, and uses the fluid concrete as the squeezing medium. The middle part of the cavity that is easily squeezed and expanded is preferentially squeezed and expanded to the maximum diameter, forming an expanded diameter cavity with small diameter expansion at the upper and lower ends and large diameter expansion in the middle part. The poured concrete is all used to squeeze and expand the pile hole wall to form the expanded diameter cavity filled with concrete. The final squeezing stress of the concrete forming the expanded diameter cavity is not less than half of the rated squeezing strength of the cavity wall of the PC pipe pile with the same outer diameter as the prefabricated hollow pile 1 under construction in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than The rated extrusion strength of the cavity wall of the constructed precast hollow pile 1, wherein the final extrusion stress of the concrete with high bearing capacity requirements for the composite pile takes a larger value, forming an equal strength zone composed of the compacted concrete 11 in the expanded diameter cavity, and a strength continuously decreasing zone composed of the compacted mixture layer 12 and the compacted rock and soil layer 13, and in the process of diffusing and attenuating the vertical pressure transmitted by the precast hollow pile 1, there is no deformation in the equal strength zone, and a stable, continuous and slow-changing deformation occurs in the strength continuously decreasing zone; then the precast hollow pile 1 is sunk into the compacted concrete 11 in the expanded diameter cavity to a certain depth or passes through the concrete in the expanded diameter cavity, the compacted mixture layer 12 and the compacted rock and soil layer 13. The rock and soil layer 13 squeezes the concrete in the hole again, further squeezes and expands the hole, squeezes and expands the compacted mixture layer 12 and the compacted rock and soil layer 13 around the compacted mixture layer 12, forming a compacted concrete enlarged body. The compacted concrete 11 inside the concrete enlarged body tightly wraps the part in contact with the outer surface of the precast hollow pile 1, the compacted mixture layer 12 wraps the compacted concrete 11 inside, and the compacted mixture layer 12 is wrapped by the compacted rock and soil layer 13 around it, i.e., a compacted concrete enlarged body. Since the rock and soil at the upper end of the columnar pile hole wall is squeezed and compacted during the downward movement of the precast hollow pile 1, it has a certain density, and the mutual contact between the circular surface at the bottom end of the columnar pile hole 4 and the bottom end of the columnar pile hole wall The large restraining force results in a large force required to compress and deform the upper and lower ends of the columnar pile hole wall. However, the middle portion of the columnar pile hole wall has a large surface area and is not affected by the rock and soil density at the upper end or the restraining force at the lower end, making it easy to deform significantly when squeezed. Furthermore, because concrete has a certain degree of fluidity, using fluid concrete as the extrusion medium prioritizes the expansion of the easily squeezed middle portion of the hole to its maximum diameter. A certain distance is maintained between two adjacent concrete expansions on a pile. The construction sequence for the concrete expansions is to construct them one by one from top to bottom. During the construction of the lower concrete expansion, the existing concrete expansion above will not be affected.

[0040] The bearing mechanism of the concrete enlargement of the present application: in the composite pile of the present application, the compacted mixture layer 12 is wrapped with the compacted concrete 11, and the compacted mixture layer 12 is wrapped with the compacted rock and soil layer 13. The content of concrete in the compacted mixture layer 12 gradually decreases from the inside to the outside, and the strength gradually decreases. The strength of the inner surface of the compacted mixture layer 12 is very close to the strength of the compacted concrete 11 wrapped inside it. The density of the compacted rock and soil layer 13 gradually decreases from the inside to the outside, and the strength also gradually decreases. The strength of the inner side of the compacted rock and soil layer 13 is very close to the strength of the outer side of the compacted mixture layer 12, and the strength of the outer side of the compacted rock and soil layer 13 is very close to the strength of the original rock and soil layer 14. It can be seen that The compacted mixture layer 12 organically combines the internal high-strength compacted concrete 11 with the external compacted rock and soil layer 13 to form a concrete expansion body. In terms of strength, the concrete expansion body can be divided into an equal-strength zone and a strength continuously decreasing zone. The equal-strength zone is the compacted concrete 11 area inside the concrete expansion body. It has a large volume and high strength. It can withstand large loads and can diffuse and attenuate the load transmission force. The strength continuously decreasing zone is composed of the compacted mixture layer 12 and the compacted rock and soil layer 13, and the strength is smoothly and continuously reduced from the inside to the outside. It has a large volume and can also diffuse and attenuate the load transmission force. It can be seen that the concrete expansion body is a region with high strength in the center and low strength in the surrounding area. The end carrier is spherical and continuously lowered from the inside to the outside; the vertical downward load force (static load test load) transmitted from the pile top is the compressed part of the equal strength zone of the concrete expansion body, and is diffused and attenuated within the umbrella-shaped body 15 below it, and is transmitted from the center to the far end. The vertical downward load force of the pile top is first transmitted to the equal strength zone of the concrete expansion body, and the larger volume of equal strength diffuses and attenuates the load force, and then transmitted to the large volume of continuous strength reduction zone, and then diffuses and attenuates. Finally, the load force that has been diffused and attenuated is transmitted to the larger original rock and soil layer 14 outside the compacted rock and soil layer 13, and then diffuses and attenuates; the equal strength zone bears a large and concentrated load force and maintains the whole The integrity of the concrete body is that the strength continuously decreasing zone bears the load force that has diffused and attenuated through the equal strength zone and continues to diffuse and attenuate. The strength of the strength continuously decreasing zone decreases smoothly from the inside to the outside, which satisfies the smooth transmission of the load force from large to small, and maintains a smooth, continuous and slow-changing deformation in the strength continuously decreasing zone, thus achieving the overall stability of the end carrier. It can be seen that the overall stability of the concrete enlarged body refers to a limit indicator that after the final extrusion pressure of the concrete forming the concrete enlarged body reaches a certain value, the concrete enlarged body diffuses and attenuates the vertical pressure (static load test load force) transmitted from the precast hollow pile 1, and there is no deformation in the equal strength zone and a smooth, continuous and slow-changing deformation occurs in the strength continuously decreasing zone.The smooth, continuous and slow-changing deformation in the strength continuously decreasing zone forms a partial settlement displacement of the composite pile, which avoids the stress concentration on the strength steep drop interface during the diffusion, attenuation and transmission of pressure, causing the low-strength surface to be damaged and produce large deformation, and the pile settlement displacement to drop sharply, resulting in excessive pile settlement (during the compressive static load test, when the current level settlement displacement is 2 times or more than the upper level settlement displacement, it is regarded as the pile settlement displacement exceeding the limit, and the test is terminated. The ultimate compressive bearing capacity of the pile is taken as the upper level test load value); therefore, the settlement displacement of the composite pile in the present application is composed of the smooth, continuous and slow-changing deformation in the strength continuously decreasing zone and the smooth, continuous and slow-changing deformation of the original rock and soil layer 14 outside the strength continuously decreasing zone, as described here. Smooth, continuous, and gradually varying deformation refers to the fact that when a composite pile is subjected to vertical pressure, no significant sudden drop in deformation occurs in the zone of continuous strength reduction and in the surrounding original rock and soil layer 14. During static compressive load tests of composite piles, within the allowable pile foundation settlement (typically 40 mm), the Q-s curve exhibits a gradual variation, with no significant sudden drop, and the tail of the s-lgt curve shows no significant downward bend. This indicates that within the compressive deformation zone of the umbrella-shaped body 15, the concrete expansion body, which achieves overall stability, experiences a gradually decreasing load from the center to the distal end, acting on the end support and surrounding original soil layer 14, where strength decreases and volume increases. This is the basis for the composite pile to avoid sudden settlement.

[0041] When forming a concrete enlarged body in the same rock and soil layer, the more concrete is poured, the greater the final extrusion pressure of the concrete forming the concrete enlarged body will be, the larger the outer diameter of the concrete enlarged body will be, the better the overall stability index of the concrete enlarged body will be, and the higher the end-bearing capacity of the concrete enlarged body will be. It can be seen that the overall stability index of the concrete enlarged body is closely related to the economy. Only emphasizing the improvement of the overall stability limit will inevitably increase the cost, which is an economic waste for this application. Under the premise of ensuring the overall stability, the continuous strength reduction zone satisfies the gradual diffusion, attenuation and transmission of the load force under the premise of reducing the economic cost, thereby ensuring the settlement stability of the composite pile.

[0042] In the composite piles of this application, there are certain requirements for the overall stability of the concrete expansion body. For rock and soil layers with greater compressibility, more concrete needs to be poured, and for rock and soil layers with less compressibility, less concrete needs to be poured. The amount of concrete poured is controlled by the final extrusion force on the concrete that forms the concrete expansion body. Through the test results of multiple groups of test piles, it is known that the pressure generated by the downward movement of the columnar weight 6 to squeeze the concrete in the cavity of the precast hollow pile 1 is not less than half of the rated extrusion strength of the cavity wall of the PC pipe pile with the same outer diameter in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than the rated extrusion strength allowed by the cavity wall of the constructed precast hollow pile 1. In the static load test of the test pile, within the allowable settlement displacement (40mm), the Q-s curve of the static load test is a slow-changing type, without a significant steep drop, and the tail of the s-lgt curve has no obvious downward bend, and the compressive limit of the test pile is The bearing capacity value is large, that is, the strength of the compacted mixture layer 12 and the compacted rock-soil layer 13 formed is sufficient to produce a smooth, continuous and slow-changing deformation during the diffusion, attenuation and transmission of the vertical load force, and no steep drop deformation will occur; otherwise, when the concrete extrusion force forming the concrete expansion body is insufficient to meet the overall stability index requirements of the concrete expansion body, when the composite pile is subjected to vertical pressure (compressive static load test), due to the insufficient strength of the compacted mixture layer 12 and the compacted rock-soil layer 13, especially in the compacted rock-soil layer 13 just below the cross-section of the equal strength zone, a large vertical steep drop deformation will occur, resulting in excessive settlement displacement of the composite pile.

[0043] In the composite pile of the present application, multiple concrete expansion bodies are relatively independent bearing bodies. Assume that the outer diameter of the compacted concrete 1 in the concrete expansion body is D, the equivalent outer diameter of the precast hollow pile is d, and the distance between the compacted concrete bodies in two adjacent concrete expansion bodies is h, where h>4D; wherein d is the outer diameter of a circular surface equal to the area enclosed by the outer edge of the cross section of the precast hollow pile 1. When the precast hollow pile 1 is a pipe pile, d is the outer diameter of the pipe pile; D is the equivalent diameter of a concrete sphere converted from the amount of concrete poured when forming the concrete expansion body. The test results of multiple groups of test piles show that when the concrete expansion body (including those that do not meet the requirements of the overall stability index) is only set at the bottom of the composite pile, the standard value of the ultimate compressive end resistance of the bottom of the composite pile is The estimation formula is:

[0044] α—The coefficient of increase in the end resistance of the concrete enlarged body. The higher the final extrusion pressure on the concrete forming the concrete enlarged body, the greater the value. The increase coefficient is related to the overall stability of the concrete enlarged body. When forming a concrete enlarged body in the same rock and soil layer, the greater the amount of concrete poured, the higher the final extrusion pressure on the concrete, the larger the outer diameter of the formed concrete enlarged body, the denser the continuous strength reduction zone of the concrete enlarged body, the higher the strength, and the stronger the ability to diffuse, attenuate and transmit load force; when the final extrusion pressure of the concrete cannot meet the overall stability index requirements for the formation of the concrete enlarged body, α takes a smaller value, usually α=1.2~1.6; when the final extrusion pressure of the concrete reaches a certain value and meets the requirements for the formation of the overall stability of the concrete enlarged body, α takes a larger value, usually α=1.8~3.5; —The standard value of the ultimate end resistance of the bearing soil layer at the bottom of the composite pile is taken according to the soil-squeezing pile.

[0045] The test results of multiple groups of test piles show that the standard value of the total ultimate end resistance of the composite piles in this application is that the concrete expansion body is set at the bottom of the pile and the concrete expansion body may or may not be set in the middle of the pile. The estimation formula is:

[0046] Where: β—Adjustment coefficient of end resistance of concrete enlarged body. When there is one concrete enlarged body in the composite pile, β=1.0; when there are two concrete enlarged bodies in the composite pile, β=0.90; when there are three or more concrete enlarged bodies in the composite pile, β=0.80; —The standard value of the ultimate end resistance of the bearing soil layer of the jth concrete enlargement in the middle of a single pile is taken according to the soil-squeezing pile.

[0047] Example 1 like Figure 1 、 Figure 2As shown, a composite pile is composed of a precast hollow pile 1 and a concrete enlargement. The composite pile has at least one concrete enlargement, which can be arranged in the middle and / or bottom of the precast hollow pile 1. The precast hollow pile 1 and the compacted concrete 11 in the concrete enlargement are consolidated into one body, and a certain distance h is maintained between two adjacent concrete enlargements. The concrete enlargement is a spherical end carrier that directly wraps a part of the outer surface of the precast hollow pile 1. The concrete enlargement is composed of an internal constant strength zone and a continuously reduced strength zone that wraps the constant strength zone. The constant strength zone is composed of compacted concrete 11, and the continuously reduced strength zone is a compacted mixture layer 12 and a compacted rock and soil layer 13. The strength of the combined structure decreases steadily and continuously from the inside to the outside. The compacted mixture layer 12 is a mixture of concrete and rock and soil with a certain thickness formed by compaction. The compacted mixture layer 12 is wrapped with an equal strength zone, and the outer periphery of the compacted mixture layer 12 is wrapped by a compacted rock and soil layer 13. In the process of diffusion and attenuation of the vertical pressure transmitted from the prefabricated hollow pile 1 by the concrete expansion body, there is no deformation in the equal strength zone, and steady and continuous slow deformation occurs in the zone of continuous strength reduction. In the static load test of the composite pile, within the allowable pile foundation settlement displacement (usually 40mm), the Qs curve of the static load test is a slow-changing type, without obvious steep drop, and there is no obvious downward bend at the tail of the s-lgt curve.

[0048] In this embodiment, the prefabricated hollow pile 1 is a prefabricated concrete hollow pile, a prefabricated steel hollow pile, or a prefabricated steel and concrete composite hollow pile.

[0049] like Figure 1As shown, a composite pile is provided with a concrete enlarged body at the bottom of the pile, and the concrete enlarged body meets the requirements of the overall stability index. When the top of the composite pile is subjected to a vertical downward pressure F, the pressure F is transmitted through the precast hollow pile 1 to the compacted concrete 11 inside the concrete enlarged body at the bottom of the pile, that is, the equal strength zone, and diffuses and decays and continues to be transmitted downward, and is successively transmitted to the compacted mixture layer 12, the compacted rock and soil layer 13, and the original rock and soil layer 14, and diffuses and decays respectively during transmission in each layer; the vertical pressure transmitted by the precast hollow pile 1 to the concrete enlarged body is the direct compression part through the equal strength zone (that is, the part below the cross section at the horizontal maximum outer diameter of the compacted concrete in the concrete enlarged body), and diffuses and decays within the umbrella-shaped body 15 below it, and is transmitted from the center to the distal end. The vertical pressure is first transmitted to the equal strength zone composed of the compacted concrete 11 in the concrete enlarged body. The pressure is then transmitted to the large volume of the continuously reduced strength zone composed of the compacted mixture layer 12 and the compacted rock and soil layer 13, and then diffused and attenuated. Finally, the pressure that has been diffused and attenuated is transmitted to the larger original rock and soil layer 14 outside the compacted rock and soil layer 13, and then diffused and attenuated. The equal strength zone bears a large and concentrated pressure and maintains its overall integrity. The continuously reduced strength zone bears the pressure that has been diffused and attenuated by the equal strength zone and continues to diffuse and attenuate the transmission. The strength of the continuously reduced strength zone decreases smoothly from the inside to the outside, which satisfies the smooth transmission of pressure from large to small, and maintains a smooth, continuous and slow deformation in the continuously reduced strength zone. Finally, the pressure transmitted to the original rock and soil layer 14 is already small. The larger original rock and soil layer 14 undergoes a smooth, continuous and slow deformation under the action of the smaller pressure.

[0050] In this embodiment, the precast hollow pile 1 is a precast concrete pipe pile, whose outer diameter is d, the outer diameter of the concrete 1 compacted in the concrete expansion body is D, and the standard value of the ultimate end resistance of the composite pile with the concrete expansion body at the bottom of the pile is The estimate is:

[0051] Where: α is the coefficient of resistance enhancement at the end of the concrete expansion body, α=1.8~3.5, and the higher the final extrusion pressure on the concrete forming the concrete expansion body, the greater the value; —The standard value of the ultimate end resistance of the bearing soil layer at the bottom of the composite pile is taken according to the soil-squeezing pile.

[0052] like Figure 2 As shown, a composite pile is provided with concrete enlarged bodies in the middle and bottom of the pile. Two concrete enlarged bodies are provided in the middle of the pile. The distance between the concrete bodies in the two adjacent concrete enlarged bodies is h, h>4D, and D is the outer diameter of the concrete 1 in the concrete enlarged body.

[0053] In this embodiment, the precast hollow pile 1 is a precast concrete pipe pile with an outer diameter of d, a concrete expansion body is set at the bottom of the pile, and two concrete expansion bodies are set in the middle of the pile. The standard value of the total ultimate end resistance of the composite pile is The estimate is:

[0054] Where: α—Concrete enlarged body end resistance enhancement coefficient, α=1.8~3.5, the higher the final extrusion pressure on the concrete forming the concrete enlarged body, the greater the value; —standard value of the ultimate end resistance of the bearing soil layer at the bottom of the composite pile; β—adjustment coefficient of the end resistance of the concrete expansion body, β=0.80; —The standard value of the ultimate end resistance of the bearing soil layer of the jth concrete expansion in the middle of the pile is taken according to the soil-squeezing pile, j=1;2.

[0055] Example 2 like Figure 3 As shown, a construction method of a composite pile with a concrete expansion body at the bottom of the pile includes the following steps: 1) Pile driving and hole pouring: Align the bottom end of the precast hollow pile 1 with the pile position, sink the precast hollow pile 1 to the top elevation of the concrete in the concrete expansion body at the bottom of the composite pile, place the spiral drill 2 concentrically into the inner cavity of the precast hollow pile 1 and rotate it to drill, first drill the rock and soil 3 that is packed at the bottom end of the inner cavity of the precast hollow pile 1, then drill the rock and soil below the precast hollow pile 1 to form a cylindrical pile hole 4, the pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile 1, lift the spiral drill 2, pour concrete 5 into the cylindrical pile hole 4 and the inner cavity of the precast hollow pile 1, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile 1 is not higher than 1.5m. Figure 3 Middle (a) to (d); 2) Forming an expanded cavity filled with concrete, a compacted mixture layer and a compacted rock and soil layer: by vertical pressure, vibration or gravity drop, the columnar weight 6 is moved downward to squeeze the concrete in the cavity of the prefabricated hollow pile 1 into the columnar pile hole 4 filled with concrete, first squeezing and expanding the rock and soil wall at the upper end of the columnar pile hole 4, then squeezing and expanding the rock and soil wall in the middle of the columnar pile hole 4, and finally squeezing and expanding the rock and soil wall at the bottom end of the columnar pile hole 4 and the rock and soil at the end face of the hole. In the process of squeezing and expanding the rock and soil of the pile hole wall, the downward columnar weight The fluid concrete is squeezed by the body 6. The fluid concrete is first squeezed to expand the rock and soil in the middle of the pile hole wall to form the largest diameter, squeezing and expanding the cylindrical pile hole 4 into a cavity with small diameter expansion at the upper and lower ends and large diameter expansion in the middle, which is filled with compacted concrete. A small amount of concrete is squeezed into the rock and soil of the cavity wall to form a compacted mixture layer 12. In the compacted mixture layer 12, the concrete content is higher on the concrete side of the cavity closer to the expanded diameter. At the same time, a certain thickness of rock and soil outside the compacted mixture layer 12 is squeezed. The compacted rock and soil layer 13 is formed. In the compacted rock and soil layer 13, the rock and soil density is greater on the side closer to the compacted mixture layer 12. The poured concrete is all used to compress the pile hole wall. The final extrusion stress of the concrete is not less than half of the rated extrusion strength of the hole wall of the PC pipe pile with the same outer diameter as the precast hollow pile 1 under construction in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than the rated extrusion strength of the hole wall of the precast hollow pile 1 under construction. The columnar weight 6 is lifted to form a spherical carrier consisting of an equal strength zone composed of the compacted concrete 11 in the expanded diameter hole, a continuously reduced strength zone composed of the compacted mixture layer 12 and the compacted rock and soil layer 13, and a spherical carrier. After the composite pile is formed, in the process of diffusing and attenuating the vertical pressure transmitted from the precast hollow pile 1, there is no deformation in the equal strength zone, and a smooth, continuous and slow-changing deformation occurs in the continuously reduced strength zone. Figure 3 in (e) ~ (i); 3) Sink the precast hollow pile 1 into the compacted concrete 11 in the expanded diameter cavity to a certain depth that meets the top elevation of the composite pile, forming a composite pile with a concrete expansion at the bottom, such as Figure 3 Middle (j). Example 3

[0056] like Figure 4 As shown, a construction method of a composite pile with a concrete expansion body at the bottom of the pile includes the following steps: 1) Drilling and pouring piles: First, use the spiral drill 2 to drill a pilot hole with a diameter smaller than the outer diameter or diagonal length of the cross section of the precast hollow pile 1 at the center of the pile position. The pilot hole is drilled to a depth below the top elevation of the concrete in the expanded concrete body at the bottom of the pile and is within the range of 1.5 to 4.0 times the outer diameter or diagonal length of the cross section of the precast hollow pile 1. Then, sink the precast hollow pile 1 at the pile position to squeeze and expand the pilot hole to the top elevation of the concrete in the expanded concrete body at the bottom of the pile. Then, pour a certain amount of concrete 5 into the inner cavity of the precast hollow pile 1 and the bottom of the pilot hole, so that the concrete pouring height of the inner cavity of the precast hollow pile 1 does not exceed 1.5m. Figure 4 Middle (a) to (d); Step 2) and step 3) are the same as step 2) and step 3) of embodiment 3. Figure 4 Middle (e)~(j).

[0057] This construction method is applicable to the construction where the outer surface of the prefabricated hollow pile 1 in the composite pile is surrounded by a low-compressible rock and soil layer, and the prefabricated hollow pile 1 cannot be directly sunk through the rock and soil layer. Example 4

[0058] like Figure 5 As shown, a construction method of a composite pile with a concrete expansion body in the middle of the pile includes the following steps: 1) Pile driving and hole pouring: Align the bottom end of the precast hollow pile 1 with the pile position, sink the precast hollow pile 1 to the top elevation of the concrete in the middle of the composite pile concrete expansion body, place the spiral drill 2 concentrically into the inner cavity of the precast hollow pile 1 and rotate it to drill, first drill the rock and soil 3 that is packed at the bottom end of the inner cavity of the precast hollow pile 1, then drill the rock and soil below the precast hollow pile 1 to form a cylindrical pile hole 4, the depth of the cylindrical pile hole 4 is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile 1, lift the spiral drill 2, pour concrete 5 into the cylindrical pile hole 4 and the inner cavity of the precast hollow pile 1, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile 1 is not higher than 1.5m. Figure 5 Middle (a) to (d); 2) Forming an expanded cavity filled with concrete, a compacted mixture layer and a compacted rock and soil layer: by vertical pressure, vibration or gravity drop, the columnar weight 6 is moved downward to squeeze the concrete in the cavity of the prefabricated hollow pile 1 into the columnar pile hole 4 filled with concrete, first squeezing and expanding the rock and soil wall at the upper end of the columnar pile hole 4, then squeezing and expanding the rock and soil wall in the middle of the columnar pile hole 4, and finally squeezing and expanding the rock and soil wall at the bottom end of the columnar pile hole 4 and the rock and soil at the bottom end face of the hole. In the process of squeezing and expanding the rock and soil of the pile hole wall, the downward columnar weight 6. The fluid concrete is squeezed. The fluid concrete is first squeezed to expand the rock and soil in the middle of the pile hole wall to form the largest diameter. The cylindrical pile hole 4 is squeezed and expanded into a cavity with small diameters at the upper and lower ends and a large diameter in the middle, which is filled with compacted concrete. A small amount of concrete is squeezed into the rock and soil of the cavity wall to form a compacted mixture layer 12. In the compacted mixture layer 12, the concrete content is higher on the side of the compacted concrete 11 in the cavity closer to the expanded diameter. At the same time, a certain thickness of the outer periphery of the compacted mixture layer 12 is formed. The rock and soil are compacted to form a compacted rock and soil layer 13. In the compacted rock and soil layer 13, the rock and soil density is greater on the side closer to the compacted mixture layer 12. The poured concrete is all used to compress the pile hole wall. The final extrusion stress on the concrete is not less than half of the rated extrusion strength of the hole wall of the PC pipe pile with the same outer diameter as the precast hollow pile 1 under construction in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than the rated extrusion strength of the hole wall of the precast hollow pile 1 under construction. The columnar weight 6 is lifted to form a spherical carrier consisting of an equal strength zone composed of the compacted concrete 11 in the expanded diameter hole, a continuously reduced strength zone composed of the compacted mixture layer 12 and the compacted rock and soil layer 13, and a spherical carrier. After the composite pile is formed, in the process of diffusing and attenuating the vertical pressure transmitted from the precast hollow pile 1, there is no deformation in the equal strength zone, and a smooth, continuous and slow-changing deformation occurs in the continuously reduced strength zone. Figure 5 in (e) ~ (i); 3) The precast hollow pile 1 is sunk through the enlarged diameter cavity filled with concrete, the compacted mixture layer 12 and the compacted rock and soil layer 13 to form a concrete enlarged body in the middle of the pile. The precast hollow pile 1 is continued to be sunk until the top elevation of the composite pile is met. The bottom of the inner cavity of the precast hollow pile 1 is filled with concrete 5 and the compacted mixture of concrete and rock and soil 7 from top to bottom to form a composite pile with a concrete enlarged body in the middle of the pile. Figure 5 Middle (j). Example 5

[0059] like Figure 6 and Figure 7 As shown, a construction method of a composite pile with two concrete expansion bodies in the middle of the pile includes the following steps: 1) Same as step 1 of Example 4), Figure 6 Middle (a) to (d); 2) Same as step 2 of Example 4), Figure 6 in (e) ~ (i); 3) Sink the precast hollow pile 1 through the enlarged diameter cavity filled with concrete, the compacted mixture layer 12 and the compacted rock and soil layer 13 to form the first concrete enlargement in the middle of the pile, such as Figure 6 middle (j); 4) Continue sinking the precast hollow pile 1 to the top elevation of the concrete in the second concrete expansion body in the middle of the pile, place the spiral drill 2 concentrically into the inner cavity of the precast hollow pile 1 and rotate it to drill, first drill the concrete 5 and the compacted rock and soil and concrete mixture 7 at the bottom end of the inner cavity of the precast hollow pile 1, then drill the rock and soil below the precast hollow pile 1 to form a cylindrical pile hole 4, the depth of which is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile 1, lift the spiral drill 2, and pour concrete 5 into the cylindrical pile hole 4 and the inner cavity of the precast hollow pile 1, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile 1 is not higher than 1.5m. Figure 7 Then repeat step 2) to form the second expanded diameter cavity filled with concrete in the middle of the pile, the compacted mixture layer and the compacted rock and soil layer, such as Figure 7 middle (n) ~ (r); 5) Repeat step 3) to form the second concrete expansion body in the middle of the pile, and continue to sink the precast hollow pile 1 until it meets the top elevation of the composite pile. The bottom of the inner cavity of the precast hollow pile 1 is filled with concrete 5 and the compacted concrete and rock-soil mixture 7 from top to bottom, forming a composite pile with two concrete expansion bodies in the middle of the pile. Figure 7 in(s).

[0060] During the construction of the composite pile, after the second concrete enlarged body in the middle of the pile is formed, the process of forming the second concrete enlarged body in the middle of the pile is repeated to form multiple concrete enlarged bodies in the middle of the pile. Finally, the precast hollow pile 1 is continued to be sunk until the top elevation of the composite pile is met. The bottom of the inner cavity of the precast hollow pile 1 is filled with concrete 5 and a mixture of compacted concrete and rock and soil 7 from top to bottom, forming a composite pile with multiple concrete enlarged bodies in the middle of the pile. Example 6

[0061] like Figure 8 and Figure 9 As shown, a construction method of a composite pile having a concrete enlarged body in the middle and a concrete enlarged body at the bottom includes the following steps: 1) 1) Same as step 1) in Example 4, Figure 8 Middle (a) to (d); 2) Same as step 2 of Example 4), Figure 8 in (e) ~ (i); 3) Sink the precast hollow pile 1 through the enlarged diameter cavity filled with concrete, the compacted mixture layer 12 and the compacted rock and soil layer 13 to form a concrete expansion body in the middle of the pile, such as Figure 9 middle (j); 4) Continue sinking the precast hollow pile 1 to the top elevation of the concrete in the concrete expansion body at the bottom of the composite pile, place the spiral drill 2 concentrically into the inner cavity of the precast hollow pile 1 and rotate it to drill, first drill the concrete 5 and the compacted rock and soil and concrete mixture 7 at the bottom end of the inner cavity of the precast hollow pile 1, then drill the rock and soil below the precast hollow pile 1 to form a cylindrical pile hole 4, the depth of which is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile 1, lift the spiral drill 2, and pour concrete 5 into the cylindrical pile hole 4 and the inner cavity of the precast hollow pile 1, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile 1 is not higher than 1.5m. Figure 9 Middle (k) ~ (m); 5) Repeat step 2) to form an expanded cavity filled with concrete at the bottom of the pile, a compacted mixture layer and a compacted rock and soil layer, such as Figure 9 middle (n) ~ (r); 6) Sink the precast hollow pile 1 into the compacted concrete 11 in the expanded diameter cavity at the bottom of the pile to a certain depth that meets the top elevation of the composite pile, forming a composite pile with a concrete expansion in the middle and a concrete expansion at the bottom, such as Figure 9 in(s). Example 7

[0062] A construction method for a composite pile having two or more concrete enlarged bodies in the middle and a concrete enlarged body at the bottom, comprising the following steps: After forming two or more concrete enlarged bodies in the middle of the pile in Example 5, proceed to Step 4) to Step 6) in Example 6 to form a composite pile with two or more concrete enlarged bodies in the middle and a concrete enlarged body at the bottom. Figure 2 shown.

[0063] like Figure 10 As shown, after the construction of embodiments 1 to 7 is completed, a certain amount of concrete 5 is poured into the inner cavity of the prefabricated hollow pile 1, and anti-pullout parts 8 are placed to form a high-pullout-resistant composite pile.

[0064] Figure 11 As shown, after the construction of embodiments 1 to 7 is completed, concrete 5 is poured into the inner cavity of the prefabricated hollow pile 1, and a steel cage 9 is placed to form a high-compression composite pile.

[0065] In the above embodiment, the enlarged cavity filled with concrete, the compacted mixture layer and the compacted rock and soil layer are formed by pouring a certain amount of concrete 5 into the cavity of the precast hollow pile 1 once and then moving the columnar weight 6 downward to squeeze the concrete. It can also be formed by pouring a certain amount of concrete 5 into the cavity of the precast hollow pile 1 twice or more and then moving the columnar weight 6 downward to squeeze the concrete twice or more, and each time the concrete 5 is poured, the columnar weight 6 is moved downward once to squeeze the concrete and expand the cavity wall.

[0066] During the construction process of the above embodiment, for the section where it is difficult to sink the precast hollow pile 1, a spiral drill 2 can be used to drill a pilot hole through the inner cavity of the precast hollow pile 1, and then the precast hollow pile 1 can be sunk through the section.

[0067] The gravity fall of the columnar weight 6 refers to the process of lifting the columnar weight 6 to a certain height multiple times and letting it fall freely multiple times during the downward movement of the columnar weight 6 after the concrete 5 is poured once. The columnar weight 6 is lifted to a certain height multiple times and then falls freely multiple times, so that the columnar weight 6 squeezes the concrete once by free fall each time it is lifted. The upper end of the columnar weight 6 is made into a cone shape with a small top and a large bottom. A lifting fixture is provided at the center of the upper end surface of the columnar weight 6 for fixing one end of a rope. The other end of the rope is fixed to the drum of the slip-type winch. A certain fitting gap (usually 40 to 65 mm) is retained between the outer surface of the columnar weight 6 and the inner cavity wall of the prefabricated hollow pile 1. The fitting gap can be used as a pouring channel to pour concrete 5 during the lifting process of the columnar weight 6 or after the columnar weight is lifted and stayed at a certain height.

[0068] The concrete 5 forming the concrete expansion body can be poured through the inner hole of the drilling tool 2 during the process of lifting the spiral drilling tool 2, or poured through the gap between the columnar weight 6 and the inner hole wall of the prefabricated hollow pile 1 during the process of lifting the columnar weight 6. The spiral drilling tool 2 or the columnar weight 6 can also be lifted to the outside of the inner hole of the prefabricated hollow pile 1 and then poured.

Claims

1. A composite pile, characterized by: The composite pile is composed of a precast hollow pile and a concrete enlarged body. There is at least one concrete enlarged body in the composite pile. The concrete enlarged body can be set in the middle and / or bottom of the precast hollow pile. The precast hollow pile and the concrete in the concrete enlarged body are consolidated into one, and a certain distance is maintained between two adjacent concrete enlarged bodies. The concrete enlarged body is a spherical end carrier that directly wraps the outer surface of the precast hollow pile. The concrete enlarged body is composed of an internal constant strength zone and a strength continuously reduced zone wrapping the constant strength zone. The constant strength zone is composed of compacted concrete, and the strength continuously reduced zone is a compacted mixed layer and a compacted mixed layer. The strength of the rock-soil layer combination decreases smoothly and continuously from the inside to the outside. The compacted mixture layer is a mixture of concrete and rock-soil with a certain thickness formed by compaction. The equal strength zone is wrapped in the compacted mixture layer, and the outer periphery of the compacted mixture layer is wrapped by the compacted rock-soil layer. In the process of diffusion and attenuation of the vertical pressure transmitted by the prefabricated hollow pile by the concrete expansion body, there is no deformation in the equal strength zone and smooth and continuous slow deformation occurs in the zone of continuous strength reduction. In the static load test of the composite pile, within the allowable pile foundation settlement displacement, the Q-s curve of the static load test is a slow-changing type, and no obvious steep drop occurs.

2. The composite pile according to claim 1, characterized in that: The prefabricated hollow piles are prefabricated concrete hollow piles, prefabricated steel hollow piles or prefabricated steel and concrete composite hollow piles; the inner cavity of the prefabricated hollow piles can be provided with pull-out members or steel cages, and a certain amount of concrete can be poured.

3. A construction method of a composite pile according to claim 1, characterized in that The steps include: 1) Pile driving and hole pouring: Align the bottom end of the precast hollow pile with the pile position, sink the precast hollow pile to the top elevation of the concrete in the concrete expansion body at the bottom of the composite pile, place the spiral drill concentrically into the inner cavity of the precast hollow pile and rotate it to drill. First, drill the rock and soil that are crowded at the bottom end of the inner cavity of the precast hollow pile, and then drill the rock and soil below the precast hollow pile to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. Raise the spiral drill and pour concrete into the pile hole and the inner cavity of the precast hollow pile, and ensure that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5m. 2) Forming an expanded cavity filled with concrete, a compacted mixture layer and a compacted rock and soil layer: Through vertical pressure, vibration or gravity drop, a columnar weight is moved downward to squeeze the concrete in the cavity of the precast hollow pile into the cylindrical pile hole filled with concrete, first squeezing and expanding the rock and soil wall at the upper end of the pile hole, then squeezing and expanding the rock and soil wall in the middle of the pile hole, and finally squeezing and expanding the rock and soil wall at the bottom end of the pile hole and the rock and soil on the bottom end face of the hole. In the process of squeezing and expanding the rock and soil of the pile hole wall, the downward-moving columnar weight squeezes the fluid concrete. The fluid concrete preferentially squeezes the rock and soil in the middle of the pile hole wall to expand to form the maximum diameter, squeezing and expanding the cylindrical pile hole into a cavity with small diameter expansion at the upper and lower ends and large diameter expansion in the middle, which is filled with compacted concrete, and a small amount of concrete is squeezed into the rock and soil of the cavity wall to form a compacted mixture layer. In the compacted mixture layer, the concrete content on the concrete side of the cavity closer to the expanded diameter is higher, and at the same time, a certain thickness of rock and soil outside the compacted mixture layer is squeezed. Densely form a compacted rock and soil layer. In the compacted rock and soil layer, the closer the rock and soil density is to the compacted mixture layer, the greater the density. The poured concrete is all used to compress the pile hole wall. The final extrusion stress on the concrete is not less than half of the rated extrusion strength of the hole wall of the PC pipe pile with the same outer diameter as the precast hollow pile to be constructed in the current industry standard "Technical Standard for Prestressed Concrete Pipe Piles" JGJ / T406-2017, and is not greater than the rated extrusion strength of the hole wall of the precast hollow pile to be constructed. The columnar weight is lifted to form a spherical carrier consisting of an equal strength zone composed of the compacted concrete in the expanded diameter hole, a continuously reduced strength zone composed of the compacted mixture layer and the compacted rock and soil layer, and a spherical carrier. After the composite pile is formed, in the process of diffusing and attenuating the vertical pressure transmitted from the precast hollow pile, there is no deformation in the equal strength zone, and a smooth, continuous and slow-changing deformation occurs in the continuously reduced strength zone. 3) Sinking the precast hollow pile into the compacted concrete in the enlarged diameter cavity to a certain depth that meets the top elevation of the composite pile; forming a composite pile with a concrete expansion at the bottom of the pile.

4. The construction method of composite pile according to claim 3, characterized in that: The step 1) is replaced by bored pile driving and pouring: first, at the center of the pile position, a pilot hole having a diameter smaller than the outer diameter or diagonal length of the cross section of the precast hollow pile is drilled using a spiral drill, and the pilot hole is drilled to a depth below the top elevation of the concrete in the expanded concrete body at the bottom of the pile and within a range of 1.5 to 4.0 times the outer diameter or diagonal length of the cross section of the precast hollow pile. Then, the precast hollow pile is sunk at the pile position to squeeze and expand the pilot hole to the top elevation of the concrete in the expanded concrete body at the bottom of the pile. Then, a certain amount of concrete is poured into the inner cavity of the precast hollow pile and the bottom of the pilot hole, so that the concrete pouring height of the inner cavity of the precast hollow pile is not higher than 1.5 m.

5. The construction method of composite pile according to claim 3, characterized in that: The method comprises the following steps: aligning the bottom end of the precast hollow pile with the pile position, sinking the precast hollow pile to the top elevation of the concrete in the expanded concrete body in the middle of the composite pile, concentrically placing the spiral drill into the inner cavity of the precast hollow pile and rotating the drill to first drill the rock and soil that are packed at the bottom end of the inner cavity of the precast hollow pile, and then drilling into the rock and soil below the precast hollow pile to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. The spiral drill is lifted and concrete is poured into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5 m. The method comprises the following steps: replacing step 3 with sinking the precast hollow pile through the expanded diameter cavity filled with concrete, the compacted mixture layer, and the compacted rock and soil layer to form the expanded concrete body in the middle of the pile. The method comprises the following steps: continuing to sink the precast hollow pile until the top elevation of the composite pile is met. Thus, a composite pile with an expanded concrete body in the middle is formed.

6. The construction method of composite pile according to claim 5, characterized in that: After step 3), the precast hollow pile is continued to be sunk to the top elevation of the concrete in the second concrete enlarged body in the middle of the pile. The spiral drill is concentrically placed in the inner cavity of the precast hollow pile and rotated to drill. The bottom end of the inner cavity of the precast hollow pile is first drilled to fill the mixture of concrete, rock and soil and concrete. Then, the rock and soil below the precast hollow pile are drilled to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. The spiral drill is lifted and concrete is poured into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5 m. Then, steps 2) and 3) are repeated to form the second concrete enlarged body in the middle of the pile. By repeating the above process of forming the second concrete enlarged body in the middle of the pile, multiple concrete enlarged bodies in the middle of the pile can be formed.

7. The construction method of composite pile according to claim 3, characterized in that: The step 1) is replaced by aligning the bottom end of the precast hollow pile with the pile position, sinking the precast hollow pile to the top elevation of the concrete in the expanded concrete body in the middle of the composite pile, concentrically placing the spiral drill into the inner cavity of the precast hollow pile and rotating it, first drilling the rock and soil that is filled at the bottom end of the inner cavity of the precast hollow pile, and then drilling the rock and soil below the precast hollow pile to form a cylindrical pile hole, the pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile, lifting the spiral drill, pouring concrete into the pile hole and the inner cavity of the precast hollow pile, and ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5m; the step 3) is replaced by sinking the precast hollow pile through the expanded diameter cavity filled with concrete, the compacted mixture layer and the compacted rock and soil layer to form a pile hole. The composite pile comprises a precast hollow pile and a composite pile having a concrete enlarged body in the middle; step 4) continuing to sink the precast hollow pile to the top elevation of the concrete in the concrete enlarged body at the bottom of the composite pile, concentrically placing the spiral drill into the inner cavity of the precast hollow pile and rotating the drill to first drill the mixture of concrete, rock and concrete that is filled at the bottom end of the inner cavity of the precast hollow pile, and then drilling the rock and soil below the precast hollow pile to form a cylindrical pile hole, the depth of the pile hole being 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile, lifting the spiral drill, and pouring concrete into the pile hole and the inner cavity of the precast hollow pile, and ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5m; then, repeating steps 2) and 3) in claim 3 to form a composite pile with a concrete enlarged body in the middle and bottom of the pile.

8. The construction method of composite pile according to claim 7, characterized in that: After step 3), the precast hollow pile is continued to be sunk to the top elevation of the concrete in the second concrete enlarged body in the middle of the pile. The spiral drill is concentrically placed in the inner cavity of the precast hollow pile and rotated to drill. The bottom end of the inner cavity of the precast hollow pile is first drilled to fill the mixture of concrete, rock and soil and concrete. Then, the rock and soil below the precast hollow pile are drilled to form a cylindrical pile hole. The pile hole depth is 1 to 3 times the outer diameter or diagonal length of the cross section of the precast hollow pile. The spiral drill is lifted and concrete is poured into the pile hole and the inner cavity of the precast hollow pile, ensuring that the pouring height of the concrete in the inner cavity of the precast hollow pile is not higher than 1.5 m. Then, steps 2) and 3) are repeated to form the second concrete enlarged body in the middle of the pile. By repeating the above process of forming the second concrete enlarged body in the middle of the pile, multiple concrete enlarged bodies in the middle of the pile can be formed.

9. The construction method of a composite pile according to any one of claims 3 to 8, characterized in that: The enlarged cavity filled with concrete, the compacted mixture layer and the compacted rock and soil layer can be formed by pouring a certain amount of concrete into the cavity of the precast hollow pile once and then moving the columnar weight downward to squeeze the concrete. It can also be formed by pouring a certain amount of concrete into the cavity of the precast hollow pile twice or more and then moving the columnar weight downward to squeeze the concrete twice or more, and each time concrete is poured, the columnar weight moves downward once to squeeze the concrete and expand the cavity wall.

10. The construction method of a composite pile according to any one of claims 3 to 8, characterized in that: Anti-pullout parts or steel cages are placed in the inner cavity of the prefabricated hollow pile, and a certain amount of concrete is poured.

11. The construction method of a composite pile according to any one of claims 3, 5, 6, 7 and 8, characterized in that: For sections where it is difficult to sink precast hollow piles, a spiral drill can be used to drill a pilot hole through the inner cavity of the precast hollow pile, and then the precast hollow pile can be sunk through the section.

12. The construction method of composite pile according to claim 9, characterized in that: The gravity fall of the columnar weight refers to the process of lifting the columnar weight to a certain height multiple times and letting it fall freely multiple times during the downward movement of the columnar weight after the concrete is poured once. The columnar weight squeezes the concrete once by free falling each time it is lifted. The upper end of the columnar weight is made into a cone shape with a small top and a large bottom. A lifting fixture is provided at the center of the columnar weight on the upper end surface for fixing one end of a rope. The other end of the rope is fixed on the drum of a slip-type winch. A certain fitting gap is retained between the outer surface of the columnar weight and the inner cavity wall of the precast hollow pile. Concrete can be poured through the fitting gap as a pouring channel during the lifting of the columnar weight or after the columnar weight is lifted and stayed at a certain height.

13. The construction method of a composite pile according to any one of claims 3 to 9, characterized in that: The concrete forming the concrete expansion body can be poured during the process of lifting the spiral drill or the columnar weight, or the spiral drill or the columnar weight can be lifted to the outside of the inner cavity of the prefabricated hollow pile and then poured.

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